This invention relates generally to apparatus and methods for process temperature control, and more particularly, to apparatus and methods for controlling process temperature with high precision.
Many processes require precise temperature control of cooling loops. This precision is critical for medical lasers and other electronic equipment where essential parameters such as frequency are affected by changes in temperature. For certain applications, minor variance in temperature-dependent properties has a detrimental effect.
High-accuracy techniques exist for low flow rates, under approximately 5 gallons per minute (gpm). One such method utilizes solenoid valves for hot and cold sources that open alternately at a high frequency to allow the hot and cold fluid to mix. A temperature sensor reports the mixed temperature to a temperature controller that compares the input signal from the temperature sensor with the controller""s setpoint temperature to determine the average time each valve is open.
Typical industrial chillers can control to approximately xc2x110xc2x0 F. High-precision industrial chiller technology exists to control to approximately xc2x11xc2x0 F. This precision is sufficient for most industrial applications, but does not meet the requirements of the applications mentioned above. It would be desirable to provide apparatus and methods to control to approximately xc2x10.1xc2x0 F., thus providing stability for temperature-critical systems and components.
In an exemplary embodiment of the invention, an apparatus includes a hot and a cold reservoir of process fluid maintained at their desired temperatures by a high-accuracy industrial chiller and an industrial heater, respectively. A three-way control valve mixes fluid from the reservoirs to produce a precisely controlled stream of process fluid delivered to the point of usage. Another flow control valve maintains system flow at a precise value.
In another embodiment, a heat exchanger upstream of the point of usage removes heat from the process stream, and in a further embodiment returns the process fluid to a reservoir with a temperature at or above the desired final temperature. Temperature control of the cooling water supplied to the heat exchanger results from a high-accuracy industrial chiller, and, in one embodiment, a reservoir on the cooling side. A two-way control valve modulates the amount of cooling water flowing through the heat exchanger, producing the final precisely-controlled fluid stream on the process side. Another flow control valve maintains system flow at a precise value.
In a further embodiment, the invention includes a pair of two-way valves to control the mixing of fluid from a hot and a cold reservoir to produce the final precisely-controlled fluid stream delivered to the point of usage. The cold and hot reservoirs are maintained at their desired temperatures by a high-accuracy industrial chiller and by an industrial heater, respectively. Another flow control valve maintains system flow at a precise value.
In yet another embodiment, the invention comprises a single reservoir of process fluid maintained slightly below the desired final temperature to be delivered to the point of usage by a high-accuracy industrial chiller. Immediately prior to the point of usage, a two-way control valve diverts a portion of the fluid through a heater loop maintained at its desired temperature by a programmable temperature controller. Another flow control valve maintains system flow at a precise value.
In a still further embodiment, refrigerant in the vapor phase is compressed and passed through an economizing heat exchanger, where it is cooled by the returning saturated vapor refrigerant. The cooled refrigerant vapor passes through an expansion valve, where most of it returns to the liquid phase, and then passes into a phase separator tank. Liquid refrigerant is pumped to the point of usage, where the heat input vaporizes the refrigerant. The refrigerant then passes back to the phase separator. Vapor from the separator then travels through the previously mentioned heat exchanger and back to the compressor inlet.